Surface modified steel member with anti-corrosion properties and method for modifying surface of steel material

ABSTRACT

A steel member with surface modified during manufacture has good anti-corrosion properties. The steel member includes a steel substrate, a metallic diffusion layer formed on the steel substrate, and an alloy deposition layer formed on the metallic diffusion layer. The steel substrate is made of medium-carbon steel or medium-carbon alloy steel. After cleaning and heating processes are applied, the metallic diffusion layer includes pearlite and ferrite crystals and hardness of the surface is also enhanced. The alloy deposition layer includes zinc ferrum alloy. The metallic diffusion layer and the alloy deposition layer have a total Micro Vickers Hardness in a range from 240 to 500.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. § 119 from China Patent Application No. 201610690168.9, filed on Aug. 19, 2016 in the China National Intellectual Property Administration, the content of which is hereby incorporated by reference. This application is a continuation-in-part under 35 U.S.C. § 120 of international patent application PCT/CN2017/091034 filed Jun. 30, 2017.

FIELD

The disclosure relates to surface modified steel members, and more particularly, to a surface modified steel member with anti-corrosion property and a method for making the same.

BACKGROUND

Corrosion of steel causes huge losses to the world. According to researches, steel which is scrapped because of corrosion every year accounts for more than 20% of annual steel production, causing a value of loss about 7000 hundred million dollars. The loss value is far more than the total loss value caused by natural calamities such as earthquake, flood, and typhoon. Nowadays, some anti-corrosion technologies are developed to ease the steel corrosion. However, the protective coatings made by the anti-corrosion technologies are not a complete answer to corrosion, and the hardness thereof is low. Nickel and zinc pretreatment technologies can allow the steel material to have higher corrosion resistance, higher wear resistance, and high vibration resistance. Thus, it is needed to use nickel and zinc pretreatment technologies to manufacture a surface modified steel structure with anti-corrosion.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the disclosure will now be described, by way of embodiments only, with reference to the attached figures.

FIG. 1 is a flowchart of an embodiment of a method for modifying surface of steel material according to the present disclosure.

FIG. 2 is a diagrammatic view of an embodiment of a surface modified steel member.

FIG. 3 is a metallographic view of a cross-section of a surface modified steel member made by steel substrate of steel No. 45 which is not quenched and tempered.

FIG. 4 is a metallographic view of a cross-section of a surface modified steel member made by steel substrate of steel No. 45 which is subjected to a quenching and tempering process.

FIG. 5 is a metallographic view of a cross-section of a surface modified steel member made by steel substrate of 42CrMoA which is subjected to a quenching and tempering process.

FIG. 6 is metallographic view of a cross-section of a surface modified steel member made by steel substrate of 35CrMo which is subjected to a quenching and tempering process.

FIG. 7 is a metallographic view of a cross-section of a surface modified steel member made by steel substrate of 35VB which is subjected to a quenching and tempering process.

FIG. 8 is metallographic view of a cross-section of a surface modified steel member made by steel substrate of 40Cr which is subjected to a quenching and tempering process.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous components. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the embodiments described herein. The drawings are not necessarily to scale and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure.

FIG. 1 illustrates an embodiment of a method for modifying surface of steel material. The method is provided by way of embodiments, as there are a variety of ways to carry out the method. Each block shown in FIG. 1 represents one or more processes, methods, or subroutines, carried out in the example method. Furthermore, the illustrated order of blocks is illustrative only and the order of the blocks can change. Additional blocks can be added or fewer blocks may be utilized or the order of the blocks may be changed, without departing from this disclosure. The method can begin at block 11.

At block 11, a steel substrate is provided, which is made of medium-carbon steel or medium-carbon alloy steel.

The medium-carbon steel includes carbon element, and the carbon element has a content in a range from 0.3% to 0.65% in the carbon steel by weight. The medium-carbon alloy steel is alloy steel including carbon element and alloy element, and the carbon element has a content in a range from 0.3% to 0.65% in the low-carbon alloy steel by weight.

In an embodiment, the steel substrate is made of one of steel No. 45, 42CrMoA, 35CrMo, 35VB, and 40Cr.

At block 12, the steel substrate is subjected to pretreatment to clean surface of the steel substrate.

In an embodiment, the pretreatment includes cleaning of oil and grease adhering to the surface, by alkaline solution, by ultrasonic waves, or by heating. The pretreatment further includes cleaning of rust on the surface, by grit blasting.

Cleaning of contaminants adhering to the surface, including the oil and the grease, and dust, avoids these contaminants being carbonized during heating. If formed, such carbonization layer might affect the appearance and the surface modification.

The alkaline solution can include a basic salt, and the basic salt includes at least one of caustic soda, sodium carbonate, sodium phosphate tribasic, sodium silicate, and sodium borate. Furthermore, the alkaline solution can further include a steel chelating agent and an organic additive agent to improve the surface cleaning. The steel chelating agent includes at least one of ethylene diamine tetraacetic acid (EDTA), sodium citrate, and triethanolamine. The organic additive agent includes at least one of ethylene glycol and ethylene glycol monoethyl ether.

Cleaning by ultrasonic waves (ultrasonic cleaning) is using ultrasound waves (usually from 20-400 kHz) to agitate washing fluid, thereby producing high forces on the oil and the grease adhering to the surface. The washing fluid can be water, or other solvents appropriate for the steel substrate to enhance the cleaning.

Cleaning by heating is heating the steel substrate to a temperature equal to or higher than the ignition point of the oil and the grease, thereby causing the oil and the grease to be burned and volatilized.

Grit blasting forcibly propels a stream of small hard balls under high pressure to remove rust and oxide skin, thereby allowing the surface to obtain desired roughness and brightness.

At block 13, a penetrating agent is provided. The penetrating agent is in a form of powders, which includes Zn powder in a range from 25% to 30% by weight, Ni powder in a range from 2% to 2.5% by weight, Al powder in a range from 1% to 2.5% by weight, rare earth metallic powder in a range from 0.5% to 1.5% by weight, ammonia chloride in a range from 1% to 4% by weight, and Al₂O₃ powder in a remaining range by weight.

Specific concentration of each type of powder in the penetrating agent can be varied according to the material of the steel substrate or the intended application of the surface modified steel structure.

At block 14, the steel substrate after the pretreatment and the penetrating agent are loaded into an enclosed steel container. The steel container is heated at a temperature in a range from 370 degrees Celsius to 430 degrees Celsius, and is rotated at a speed in a range from 5 Revolutions Per minute (RPM) to 10 RPM during the heating. By conduction heating of the penetrating agent and the steel substrate, the steel substrate and the penetrating agent can be at same temperature, and the penetrating agent can penetrate into the steel substrate to modify the surface of the steel substrate.

The speed for rotating the steel container ensures even heating of the penetrating agent and the steel substrate. Thus, the penetrating agent evenly penetrates into the steel substrate. The temperature for heating the steel container is also important, a higher temperature provides a significantly larger penetrating rate by the atoms in the penetrating agent. The specific temperature for heating can be varied according to the material of the steel substrate or the intended application of the surface modified steel member.

In an embodiment, a time period for heating the steel container (that is, a time period for the surface modification) is in a range from 1 hour to 10 hours. The specific time period for heating the steel container can also be varied according to the material of the steel substrate or the intended application of the surface modified steel member.

In an embodiment, the steel substrate can be preheated to a temperature from 400 degrees Celsius to 420 degrees Celsius, and the preheated steel substrate and the penetrating agent are mixed and loaded into the steel container. In other embodiments, the steel substrate is not preheated, and the steel substrate and the penetrating agent are both at room temperature when loaded into the steel substrate.

At block 15, the steel substrate after surface modification is washed, thereby obtaining the surface modified steel member.

In an embodiment, the steel substrate after surface modification is allowed to naturally cool. After removing dust on the surface, the steel substrate is then washed by water to remove remaining powders and other impurities.

FIG. 2 illustrates an embodiment of a surface modified steel member 100 with anti-corrosion properties. The surface modified steel member 100 includes a steel substrate 10, a metallic diffusion layer 20 formed on the steel substrate 10, and an alloy deposition layer 30 formed on the metallic diffusion layer 20. The metallic diffusion layer 20 defines a transition region between the steel substrate 10 and the alloy deposition layer 30. The metallic diffusion layer 20 includes pearlite crystals and ferrite crystals. The alloy deposition layer 30 includes zinc ferrum alloy. In an embodiment, the thickness of the metallic diffusion layer 20 is in a range from 30 microns to 120 microns. The thickness of the alloy deposition layer 30 is in a range from 60 microns to 110 microns.

The metallic diffusion layer 20 and the alloy deposition layer 30 have a total Micro Vickers Hardness in a range from 240 to 500. If the steel substrate 10 is not quenched and tempered before surface modification, the metallic diffusion layer 20 has a Micro Vickers Hardness greater than a Micro Vickers Hardness of the steel substrate 10. In another embodiment, if the steel substrate 10 is subjected to a quenching and tempering process beforehand, quenching and tempering structures, such as tempered sorbate, are formed on the surface of the steel substrate 10. The metallic diffusion layer 20 has a Micro Vickers Hardness not greater than a Micro Vickers Hardness of the steel substrate 10.

In an embodiment, the concentration of the pearlite crystals in the metallic diffusion layer 20 decreases along a direction from the alloy deposition layer 30 to the steel substrate 10. The concentration of the ferrite crystals in the metallic diffusion layer 20 increases along the direction from the alloy deposition layer 30 to the steel substrate 10. In an embodiment, the concentration of the pearlite crystals in a region of the metallic diffusion layer 20 facing the alloy deposition layer 30 is in a range from 70% to 90%. The concentration of the ferrite crystals in the region is in a range from 10% to 30%.

Embodiment 1

A steel substrate of steel No. 45, not quenched and tempered, was provided. The steel substrate was subjected to a pretreatment, including cleaning of oil and grease by alkaline solution and removal of rust by grit blasting. A penetrating agent was provided, including Zn powder of 30% by weight, Ni powder of 2% by weight, Al powder of 2.5% by weight, rare earth metallic powder of 0.5% by weight, ammonia chloride of 4% by weight, and Al₂O₃ powder of 61% by weight. The steel substrate after the pretreatment and the penetrating agent were both at room temperature when loaded to an enclosed steel container. The steel container was heated at a temperature at 400 degrees Celsius for 1 hour, and was rotated at a speed of 5 RPM during the heating to perform surface modification. The steel substrate after surface modification was washed by water to obtain the surface modified steel member.

FIG. 3 shows that the surface modified steel members in the Embodiment 1 includes two metallographic structural layers formed on the steel substrate, that is, an outer alloy deposition layer and an inner metallic diffusion layer. Referring to FIG. 3, the color of the pearlite crystals in metallic diffusion layer is lighter than the color of the pearlite crystals in the steel substrate. The thickness of the metallic diffusion layer is 100 microns.

The concentration of the pearlite crystals in the metallic diffusion layer decreases along a direction from the alloy deposition layer to the steel substrate. The concentration of the pearlite crystals in a region of the metallic diffusion layer facing the alloy deposition layer is 70%. The concentration of the ferrite crystals in the metallic diffusion layer increases along the direction from the alloy deposition layer to the steel substrate. The concentration of the ferrite in the region is 30%.

The surface modified steel member was subjected to an etching process by immersing the surface modified steel member in an etchant including nitric acid and alcohol, with a concentration from 1% to 5%. Results show that a bright white color remains on the metallic diffusion layer after 20 seconds to 50 seconds, indicating that each surface modified steel member has a good corrosion resistance.

Embodiment 2

Five steel substrate of steel No. 45, 42CrMoA, steel 35CrMo, steel 35VB, and steel 40Cr were also provided. Differences from the Embodiment 1 is that:

(1) In this embodiment, a penetrating agent was provided, including Zn powder of 25% by weight, Ni powder of 2.5% by weight, Al powder of 1% by weight, rare earth metallic powder of 1.5% by weight, ammonia chloride of 1% by weight, and Al₂O₃ powder of 69% by weight.

(2) In this embodiment, each of the five steel substrates was subjected to a quenching and tempering process.

Then, each of the five steel substrates was subjected to the same pretreatment and the same surface modification as in Embodiment 1, to obtain the surface modified steel members.

FIGS. 4 to 8 show that each of the five surface modified steel members in the Embodiment 2 also includes two metallographic structural layers formed on the steel substrate, that is, an outer alloy deposition layer and an inner metallic diffusion layer. The thickness of the metallic diffusion layer is in a range from 30 microns to 100 microns. The quenching and tempering process for the steel substrate forms quenching and tempering structures in the metallic diffusion layer.

Each of the five surface modified steel members was subjected to an etching process by immersing the surface modified steel member in an etchant including nitric acid and alcohol, with a concentration from 1% to 5%. Results show that a bright white color remains on the metallic diffusion layer after 20 seconds to 50 seconds, indicating that each surface modified steel member has a good corrosion resistance. Each of the two surface modified steel members were further subjected to a neutral salt spray (NSS) test and a sulfur dioxide test. Results show that the surface-modified steel member generates no red rust after 2000 hours in the NSS test, and also generates no red rust after 240 hours in the sulfur dioxide test, which further indicating that each surface modified steel member has good corrosion resistance.

Furthermore, the hardness of each of the five surface modified steel members was further tested. Results show that the Micro Vickers Hardness of the metallic diffusion layer is slightly less than the Micro Vickers Hardness of the steel substrate after being quenched and tempered. The metallic diffusion layer and the alloy deposition layer have a total Micro Vickers Hardness in a range from 240 to 500. Moreover, the concentration of the pearlite crystals in the metallic diffusion layer decreases along a direction from the alloy deposition layer to the steel substrate. The concentration of the pearlite crystals in a region of the metallic diffusion layer facing the alloy deposition layer is in a range from 80% to 90%. The concentration of the ferrite crystals in the metallic diffusion layer increases along the direction from the alloy deposition layer to the steel substrate. The concentration of the ferrite crystals in the region is in a range from 10% to 20%.

The surface modified steel structure according to the present disclosure has a good corrosion resistance, which can reduce the losses caused by steel corrosion. Furthermore, the basic mechanical properties of the steel substrate are not changed, but the abrasion resistance of the steel substrate is improved because of the high hardness imparted by these processes.

The embodiments shown and described above are only examples. Therefore, many commonly-known features and details are neither shown nor described. Even though numerous characteristics and advantages of the present technology have been set forth in the foregoing description, together with details of the structure and function of the present disclosure, the disclosure is illustrative only, and changes may be made in the detail, including in matters of shape, size, and arrangement of the parts within the principles of the present disclosure, up to and including the full extent established by the broad general meaning of the terms used in the claims. It will, therefore, be appreciated that the embodiments described above may be modified within the scope of the claims. 

What is claimed is:
 1. A surface modified steel member with anti-corrosion properties, comprising: a steel substrate made of medium-carbon steel or medium-carbon alloy steel, the steel substrate comprising carbon element which has a content in a range from 0.3% to 0.65% in the steel substrate by weight; a metallic diffusion layer formed on the steel substrate, the metallic diffusion layer comprising pearlite crystals and ferrite crystals; and an alloy deposition layer formed on the metallic diffusion layer opposite to the steel substrate, the alloy deposition layer comprising zinc ferrum alloys; wherein the metallic diffusion layer and the alloy deposition layer have a total Micro Vickers Hardness in a range from 240 to
 500. 2. The surface modified steel member of claim 1, wherein the steel substrate is not quenched and tempered, and the metallic diffusion layer has a Micro Vickers Hardness greater than a Micro Vickers Hardness of the steel substrate.
 3. The surface modified steel member of claim 1, wherein the steel substrate is quenched and tempered, and the metallic diffusion layer has a Micro Vickers Hardness not greater than a Micro Vickers Hardness of the steel substrate.
 4. The surface modified steel member of claim 3, wherein the metallic diffusion layer further comprises quenching and tempering structures.
 5. The surface modified steel member of claim 4, wherein the quenching and tempering structures comprise tempered sorbate.
 6. The surface modified steel member of claim 1, wherein a thickness of the metallic diffusion layer is in a range from 30 microns to 120 microns, and a thickness of the alloy deposition layer is in a range from 60 microns to 110 microns.
 7. The surface modified steel member of claim 1, wherein a concentration of the pearlite crystals in the metallic diffusion layer decreases along a direction from the alloy deposition layer to the steel substrate, and a concentration of the ferrite crystals in the metallic diffusion layer increases along the direction from the alloy deposition layer to the steel substrate.
 8. The surface modified steel member of claim 7, wherein the concentration of the pearlite crystals in a region of the metallic diffusion layer facing the alloy deposition layer is in a range from 70% to 90%, and a concentration of the ferrite crystals in the region is in a range from 10% to 30%.
 9. A method for modifying surface of steel material, comprising: providing a steel substrate which is made of medium-carbon steel or medium-carbon alloy steel, the steel substrate comprising carbon element which has a content in a range from 0.3% to 0.65% in the steel substrate by weight; pretreating the steel substrate to clean surfaces of the steel substrate; providing a penetrating agent, the penetrating agent comprising Zn powder in a range from 25% to 30% by weight, Ni powder in a range from 2% to 2.5% by weight, Al powder in a range from 1% to 2.5% by weight, rare earth metallic powder in a range from 0.5% to 1.5% by weight, ammonia chloride in a range from 1% to 4% by weight, and Al₂O₃ powder in a remaining range by weight; loading the steel substrate after the pretreatment and the penetrating agent into an enclosed steel container, heating the steel container to a temperature in a range from 370 degrees Celsius to 430 degrees Celsius, and rotating the steel container at a speed in a range from 5 RPM to 10 RPM during the heating, thereby causing the penetrating agent to diffuse into the steel substrate to modify the surface of the steel substrate; washing the steel substrate after the surface modification, thereby obtaining the surface modified steel member.
 10. The method of claim 9, wherein the pretreating method comprises cleaning of oil and grease adhering to the surface with alkaline solution, cleaning by ultrasonic waves, or by heating, and the pretreatment further comprises cleaning of rust on the surface by grit blasting.
 11. The method of claim 9, wherein the steel substrate is preheated to a temperature from 400 degrees Celsius to 420 degrees Celsius before loading into the enclosed steel container, and the preheated steel substrate and the penetrating agent are mixed followed by being loaded into the steel container.
 12. The method of claim 9, wherein the steel substrate and the penetrating agent are both at a room temperature when loaded into the steel container.
 13. The method of claim 9, wherein the steel substrate is quenched and tempered to form quenching and tempering structures on the steel substrate before the pretreatment.
 14. The method of claim 9, wherein a time period for heating the steel container is in a range from 1 hour to 10 hours.
 15. The method of claim 9, wherein the steel substrate after surface modification is air cooled before washing. 